Serial communication

[Se]

Hello,
I’m trying to get data from the instrument (HMP230 series transmitter) and display on PC, using serial communication. I use write and read VISA to send the command to the port in order to read data back from the instrument, but whatever command I sent e.g. “R” or “SEND” to the port is what I received back. Does anyone know what the problem is?

[Ray K]

If you are using RS-485 then you may have configured your serial port to recieve echoes of your transmissions.For more infor, see the section on tranciever modes the Serial user manual

If you are using RS-232, then there may be a short between your transmit and recieve lines(pins 2&3).

Of course your instrument's normal operation procedure may be to echo back commands. For example, a normal response to "temp?\n" may be "temp?\n100C\n". In this case, you would read twice. The first read would get "temp?\n" and the second read would recieve the "100C\n".

[Ray K]

Message from SE

"Thanks Ray,
I use terminal.exe from win 3.1 to send the command “SEND” to the port and the reading values of the instrument are returning back. Does it mean that there’s a problem with the transmit and receive line(2&3) or any other possible problems?"

Response from Ray K:
So from what I gather, you have VISA installed on a Win 3.1 machine. When you write and read with VISA, you read you own commands back, but when you use terminal.exe to communicate, you get numbers back?